This invention relates to a machine for butting together two metal bands running after one another and a method for implementing such a machine.
In metallurgical installations, in particular in metal band production lines, we must often resort to connecting the ends of both successive bands by electric welding. For example, in band treatment installations, the said bands are generally wound into coils to go from operation to the next. To perform continuous work, for example in finishing lines, the downstream end must therefore be welded, in the running direction, of a band at the end of a treatment with the upstream end of the following band. We are then led to weld along a transversal line, generally perpendicular to the running axis.
Different means are used for this purpose. We can, for example, apply the ends of two bands over one another, but it is often necessary to butt-weld both bands, without any excessive thickness. In the butt welding process, both ends are shorn first of all, respectively downstream and upstream, of both bands, along two parallel lines, and the bands are then brought closer to one another so that the facing edges, heated at a certain temperature at which welding can take place, are made to contact each other.
Such an installation comprises therefore, generally speaking, means for shearing both parallel edges, means for applying both shorn edges towards one another and means for heating the ends of both edges in engagement, at a temperature where welding can take place.
For shearing and welding, both ends, respectively downstream and upstream of both bands are, generally, held by locking members mounted on both stands, respectively fixed and mobile, whereas each locking member comprises two vices provided with clamping jaws placed, respectively, on either side of a running plane of the bands, whereas at least one of the vices can be moved vertically from a position where the jaws are spaced apart to allow the bands to run, to a position where the jaws are close. to one another to hold the band.
In a known embodiment described, for example, in the document EP-A-0.135.133, the tools used, respectively, for shearing the edges and for welding, are placed after one another along the longitudinal running direction of the bands.
Such an arrangement increases the length of the machine and requires displacement of both bands from a shearing zone to a heating zone. Moreover, misalignments are possible during this transfer.
It has therefore been suggested that shearing and welding should be performed at the same location, whereas both bands remain locked between the jaws. In an arrangement often used, both locking members are connected respectively, to two terminals of an electric power source, and heating is conducted by forming short-circuits between two facing edges of both bands placed at different potentials. This is the so-called flash butt welding mode.
It is preferable, however, to apply over one another, under a certain pressure, the ends of both bands in order to provide a forging effect during welding. For an installation of this type described, for example, in the document EP-A-0.168.837, both locking members connected to an electric power source are therefore mounted on two locking stands, respectively, a fixed stand and a mobile stand that can be moved longitudinally with respect to one another.
Such installations are now used widely and have been subjected to various improvements.
For instance, in the arrangement described in document FR-A-2.756.504, all the operations can be conducted in a same working position between both locking members of the ends of both bands. Indeed, the various tools necessary for welding, such as shears and a planer, are placed on a tool carriage that can be moved longitudinally beside both stands of the machine, and connected to sliding means that enable to bring the various tools one after the other in the common working position.
However, the flash butt welding process is not applicable to all metals. In particular, for certain special steels, added elements may be oxidised, which makes the welded spots brittle. Moreover, the necessary increase in temperature may cause excessive hardening of the welded section.
Thus, we have been led to develop other welding modes. In particular, it is sometimes advantageous to use a laser torch emitting an extremely thin beam, which enables to reduce the zone affected by the welding.
In practice, however, conventional flash butt welding remains preferable for metals produced usually, whereas laser welding is provided for particular products.
Still, such products represent weights that, often, do not justify the realisation of a specific installation.
It is therefore interesting to have, in the same installation, means enabling, in order to suit requirements, to perform the welding operation, either flash butt welding or laser welding or even via another process.
However, modern installations are subject to conflicting requirements. On the one hand, they should meet the quite various needs of the clientele that, often, cannot be anticipated sufficiently in advance. On the other hand, for reasons of profitability, the bands run at high speed and downtimes, causing costly loss of production, should be avoided or, at least, reduced as far as possible.
Besides, we have also noticed that another difficulty was linked to the fact that the arrangements intended for flash butt welding do not comply necessarily with the requirements of the laser welding mode. In particular, it is necessary, in all cases, that the edges to be welded should be rectilinear and parallel but, in flash butt welding, a certain cantilever distance should be left between the shorn edge and the end of the clamping jaws to enable welding. The result can be slight deformation of the sheet metals that cannot ensure rectitude and sufficient parallelism of the edges for laser welding using a beam with very reduced sizes.
The purpose of the invention is to solve all these problems thanks to new arrangements that enable to change welding mode very quickly while having means available that enable, in all cases, to perform the welding operation under the best conditions.
The invention relates therefore, generally speaking, to a machine for butting together metal bands comprising two locking stands that can be moved longitudinally with respect to one another, on which are mounted, respectively, two members for locking, respectively, the downstream end, in the running direction, of a first band and the upstream end of a second band, each comprising, on either side of a running plane of the bands, two vices on which are fixed, in a removable fashion, two pairs of jaws for clamping, respectively, the end of each band, whereas the said vices can be moved from a spaced apart position in which the jaws can be removed, and a close position, and means for welding two parallel edges provided respectively on the said ends, respectively downstream and upstream, of both bands, after bringing the said edges closer to one another by longitudinal displacement of the said locking members towards one another, whereas the said welding means operate respectively at least according to two different welding modes.
According to the invention, the machine is provided with at least two clamping jaw assemblies suitable, for each assembly, respectively to each welding mode, whereas the said clamping jaws are mounted in order to slide over each corresponding vice and connected with transfer means, respectively of a first jaw assembly from a working position centred on the running axis to a laterally spaced apart standby position and of a second assembly, from a standby position to the working position.
The invention also relates to a butting method in which it is possible to weld two successive bands according to either of at least two different welding modes in relation to the nature and/or the thickness of the bands.
For this purpose, we have two clamping jaw assemblies suitable respectively to each welding mode and, when changing welding modes, the first jaw assembly used previously for welding according to a first mode is removed from the machine and replaced with the second jaw assembly suitable to the second welding mode, whereas the latter method may then take place under the best conditions.
In a particularly advantageous embodiment, the machine comprises a central guiding assembly comprising, on each stand, a pair of guiding paths provided respectively on both vices of each locking member and comprising each at least one supporting rail sliding, respectively for each jaw of the corresponding locking member, whereas each central guiding path extends transversally to the running direction, between two lateral sides of the stand of the machine and the said machine is connected with at least one standby chassis placed on at least one side of the machine and carrying at least one lateral guiding assembly comprising two pairs of guiding paths respectively for both jaws of each locking member each comprising at least one rail placed respectively in the extension of the corresponding rail of the corresponding vice, at least in a relative position of the standby chassis with respect to both stands to allow transfer, by sliding on the aligned rails, of a first clamping jaw assembly from their working position to the standby chassis and, conversely, of a second clamping jaw assembly from the standby chassis to the working position.
In a preferred embodiment, the machine comprises two lateral guiding assemblies, respectively, a first lateral assembly that is empty initially for the reception of a first clamping jaw assembly from the working position by sliding over the aligned rails, respectively of the central guiding assembly of the said first lateral assembly, and a second lateral guiding assembly for standby support of a second clamping jaw assembly and transfer of the said clamping jaws into the working position after retraction of the said jaw assembly and alignment of the rails of the said second lateral assembly with those of the central guiding assembly.
Thus, a first clamping jaw assembly is mounted, in working position, on the central guiding assembly and a second clamping jaw assembly is mounted in standby position on the rails of a lateral guiding assembly provided on a second standby chassis, whereas the machine comprises means for simultaneous transfer of the second jaw assembly from its standby position to the working position on the central guiding assembly with retraction of the first jaw assembly and transfer of the said assembly from its working position to a standby position on a lateral guiding assembly provided on a first standby chassis, on the other side of the machine.
Usually, each locking member comprises two vices on which are mounted, respectively both clamping jaws, whereas the said vices are movable with respect to one another perpendicular to the running plane from a position for clamping the jaws and a spaced apart position.
In such an arrangement, the rails of both lateral guiding assemblies are placed at levels corresponding respectively to the levels of the rails of the central assembly provided respectively on both vices of each locking member, in the position where the clamping jaws are spaced apart, in order to allow replacement of the said jaws while passing, respectively, above and below the running plane of the bands.
Thanks to this arrangement, the jaws can be replaced when the vices are spaced apart, by sliding the jaws, respectively above and below the band and without engagement with the said band. Thus, when changing welding mode between the downstream end of a first band and the upstream end of a second band, the first jaw assembly placed in the machine and suitable to the previous welding mode can be removed from the machine and replaced with a second assembly suitable to the following welding mode, as the first band is running to an end and without stopping the said from running.
The machine according to the invention enables, in particular, either flash butt welding or laser welding. The machine comprises then two clamping jaw assemblies, respectively a first jaw assembly suitable to flash butt welding and each comprising a removable fastening section on the corresponding lengthened vice, on the side of the edge to be welded, by quite a thick lip to enable application of a forging pressure between the edges to be welded and a second jaw assembly suitable to laser beam welding and each comprising a removable fastening section on the lengthened vice, on the side of the edge to be welded, by a nose extending to the vicinity of the edge to be welded in order to maintain the band over its whole width during the shearing process, whereas the said nose is rather thin to allow passage of a laser beam emitting torch.